Beta-hydroxy fatty acid production during normal and ischemic perfusion will be measured in the isolated perfused heart (rabbit) and in the in situ dog heart. Gas liquid chromatography-mass spectrometry will be used to identify and measure the beta-hydroxy fatty acids produced and released by these hearts. Beta-hydroxy fatty acid production will be related to the degree and duration of ischemia, coronary perfusate free fatty acid content, and coronary perfusion with other metabolites and metabolic inhibitors. Beta-hydroxy fatty acid production will be studied also during fatty acid oxidation by isolated heart mitochondria.